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ALT ACQ Mode - Change of Selected Altitude During the Arming Phase Figure 013
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ALT ACQ Mode - Change of Selected Altitude During the Capture Phase
Figure 014
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Barometric Correction
Figure 015
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4
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5
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-each FMGC utilizes either the standard altitude or the corrected altitude of the barometric pressure that the ADCs supply. Thus, in BARO (QNH) selection, the captured altitude corresponds to an altitude with respect to the sea level. In standard selection, the captured altitude corresponds to a level in the standard atmosphere.
Elaboration of orders (Ref. Fig. 016) In order to be sure that the level is reached, a fixed value Zo = plus or minus 40 ft brings an adequate correction to the target altitude. In order to homogenize the duration of capture according to the initial VZBI and to avoid overshoots, the gain FVZ is elaborated with the initial VZ and kept constant during the phase.
Operational logic
a Altitude acquire mode armed.
_ The ALT ACQ mode can be armed provided that:
-The modes below are not active: ALT ACQ ALT G/S Capture G/S Track Final Des Land Track V/S FPA when the selected V/S FPA reference is such that the aircraft deviates from the selected altitude reference. PITCH TO or PITCH GA when FCU level is lower than aircraft level.
-After FCU level capture, a new level is selected or there is a difference greater than 250 ft between the aircraft level and the level selected on the FCU.
b Altitude acquire mode active
_ With the ALT ACQ mode armed, the ALT ACQ mode is activated if one of the conditions below is present:
-
the capture condition of the FCU level is met. In this case, the light which indicates the automatic level change on the FCU will go off.
-
the condition for capture of the altitude constraint provided by the FMS is met.
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ALT ACQ Control Law
Figure 016
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NOTE : The altitude acquisition mode is inhibited when a
____ level is selected or below 400 ft with the Pitch Takeoff or Pitch Go Around modes active.
(b) Altitude hold mode (ALT HOLD)
1_ Characteristics
This mode permits to hold the altitude selected on the FCU or
the altitude constraint delivered by the FM part.
2_ Operational use
The engagement of the ALT mode is automatic when, with the ALT
ACQ mode active, the difference between the aircraft altitude
and the target altitude becomes lower than 20 ft.
(Ref. Fig. 012)
The level held in ALT mode is the altitude memorized upon
engagement of the mode. Then it is not affected by a change of
reference in the ALT window of the FCU display or by a change
of barometric correction.
With the ALT mode active on the FD, engagement of the AP
causes:
- engagement of the ALT ACQ mode and capture of the selected
level if the difference between the selected level and the
aircraft level is lower than 250 ft.
- if, at AP engagement, the difference between the aircraft
level and the selected level is greater than 250 ft., the AP
holds the altitude obtained after cancellation of the vertical
speed.
(Ref. Fig. 017)
3_ Elaboration of orders
(Ref. Fig. 018)
The Delta Vc curve corresponds to the "ALT Soft" mode.
In the case of flight at high speeds in ALT mode on the AP/FD
and Mach hold by the autothrust, it is permitted, if
disturbances are present, to have a plus or minus 50 ft
altitude variation in order to keep the speed constant and
then minimize fuel consumption.
4_ Operational logic
The altitude hold mode becomes active if, with the altitude
acquire mode engaged, the condition for changing to the
altitude mode is met.
When the altitude mode is active, it can engage two different
sub-modes:
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